GSM is a portable telephone system in Europe, and DCS is a personal mobile communications system in Europe. Both of them use a TDMA (Time Division Multiple Access) system. Also, as a modulation method, they use a Gaussian filter for a transmission baseband filter and use GMSK (Gaussian-filtered Minimum Shift Keying) that is a narrow band MSK (Minimum Shift Keying) in which a band is limited. However, each system employs a different frequency band.
FIG. 1 shows a configuration of a conventional GSM terminal device 200. This GSM terminal device 200 processes a transmission/reception signal in a 900 MHz band. On the contrary, a device that processes a transmission reception signal in an 1800 MHz band is a DCS terminal device. Both of them have the substantially similar configurations.
At first, a transmitting system 200T of FIG. 1 is explained. A transmission data generated in a data generating unit (not shown) is sent to a baseband processing unit 201. The baseband processing unit 201 performs a phase modulating process on the transmission data, generates an I signal and a Q signal, which are orthogonal to each other, and sends to a quadrature modulation unit 202. In the quadrature modulation unit 202, the I signal and the Q signal, which are inputted thereto, are mixed with an intermediate frequency signal (hereafter, referred to as an IF signal) generated by a fixed PLL (Phase Locked Loop) circuit 203, respectively, and synthesized and then sent to an offset PLL circuit unit 204.
The offset PLL circuit unit 204 generates an RF signal (Radio Frequency signal) in a 900 MHz band that is orthogonally modulated. At this time, the offset PLL circuit unit 204 is a frequency synthesizer for offset PLL, and a signal is sent thereto from a channel PLL circuit unit 209 for generating a receiving local oscillation signal, which will be described later.
The RF signal generated by the offset PLL circuit unit 204 is amplified at a predetermined gain by a constant gain amplifier 205, and then amplified by a power amplifier 206, and further radiated through an antenna switch 207 from an antenna 208 to air.
A receiving system 200R will be described below. The RF signal transmitted from a base station is received through the antenna 208 and the antenna switch 207, and sent to a band pass filter 211 and filtered. A filtering output of the band pass filter 211 is amplified by a low noise amplifier 212, and then sent to a quadrature demodulation unit 213.
The quadrature demodulation unit 213 demodulates the I signal and the Q signal, which are the baseband signals, from the amplification output from the low noise amplifier 212. At this time, the quadrature demodulation unit 213 receives the receiving local oscillation signal, which is used for the demodulation, from the channel PLL circuit unit 209.
Next, portions including the quadrature modulation unit 202, the fixed PLL circuit unit 203, the offset PLL circuit unit 204 and the channel PLL circuit unit 209 in FIG. 1 will be described in detail with reference to FIG. 2.
The fixed PLL circuit unit 203 includes a VCO (Voltage Controlled Oscillator) 221, a fixed PLL controlling unit 222 and a low pass filter 223, and generates an intermediate frequency signal of 760 MHz, and sends to a quadrature modulation unit 222.
The quadrature modulation unit includes a divider 224, mixers 225, 226 and an adder 227. The divider 224 divides the intermediate frequency signal of 760 MHz from the fixed PLL circuit unit 203 into halves, and makes into intermediate frequency signals of 380 MHz of two phases different from each other by 90 degrees, and then sends to the mixer 225 and the mixer 226.
The mixers 225 and 226 mix the I signal and the Q signal with the intermediate frequency signals of 380 MHz of the two phases whose phases are different by 90 degrees, respectively. Then, in the quadrature modulation unit 202, outputs of the mixers 225 and 226 are added by the adder 227 and sent to the offset PLL circuit unit 204.
The offset PLL circuit unit 204 includes a VCO 228, a mixer 229, a low pass filter 230, a phase comparator 231 and a low pass filter 232. Also, the channel PLL circuit unit 209 includes a VCO 233, a channel PLL 234 and a low pass filter 235.
The channel PLL circuit unit 209 generates a signal of a suitable frequency at a time of transmission from the VCO 233 or at a time of reception, in coincidence with a frequency of a channel used by the GSM terminal device 200. In the case of this example, at the time of the transmission, it generates a transmission signal of 1260 to 1295 MHz, and sends to the offset PLL circuit unit 204. Also, at the time of the reception, it generates an oscillation frequency signal of 1387.5 to 1440 MHz, which is outputted as a receiving local oscillation signal from an output terminal 236.
In the offset PLL circuit unit 204, at the time of the transmission, an oscillation output signal of the VCO 228 and a transmission frequency signal for a channel to be used from the channel PLL circuit unit 209 are mixed by the mixer 229, and its mixed output is sent through the low pass filter 230 to the phase comparator 231. The phase comparator 231 sends the phase comparison output between the output from the low pass filter 230 and the output from the quadrature modulation unit 202, through the low pass filter 232 to the VCO 228, and a frequency of an output oscillation signal from this VCO 228 is controlled.
Accordingly, an oscillation frequency of the VCO 228 is converged so as to be equal to a value obtained by the following calculation: (the oscillation frequency of the VCO 233)−{(the oscillation frequency of the VCO 221)/2}. The IF signal of 380 MHz from the quadrature modulation unit 202, which is inputted to the phase comparator 228, has the phase information for the I signal and the Q signal. Thus, the output signal of the VCO 228 is also phase-modulated by the I signal and the Q signal. That is, as the output of the VCO 228, the transmission signal of the GSM is GMSK-modulated and directly obtained.
The circuit for the transmission signal generation using the offset PLL circuit unit 204 as mentioned above can be attained by a fact that the GMSK modulation is the modulating method using the information of only the phase.
By the way, recently, a technique of CDMA (Code Division Multiple Access) or W-CDMA (Wideband Code Division Multiple Access) being a leading system as a next generation of a mobile communication system has been remarked. In this specification description, the communication method employing the W-CDMA system and the like is assumed to be a UMTS (Universal Mobile Telecommunication System) system.
In the case of the UMTS (Universal Mobile Telecommunication System) system, as the modulating method, it does not use the modulating method through the information of only the phase such as the GMSK, and it uses HPSK that is the modulating method using even information of an amplitude and the like.
From the background that there are the plurality of communication methods and the plurality of communication service frequency bands, as described above, a multi-band radio signal transmitter/receiver has been desired which can be used as a multi-band system based on two kinds of communication methods including the function of the GSM terminal device and the function of the DCS terminal device as mentioned above and even the function of the W-CDMA terminal device.
However, the W-CDMA employs the modulating method such as HPSK and the like. Thus, if a multi-band system terminal including therein the above-mentioned GSM terminal device 200 is considered, the transmission signal orthogonally modulated by the above-mentioned offset PLL circuit unit 204 can not be generated. This is because the QPSK, the HPSK and the like have the information of amplitude components. In the output signal of the VCO 228 of FIG. 2, it is evident that correspondingly to an output voltage level of the phase comparator 231, only its phase component is changed, and the change in the amplitude is not induced at all.
FIG. 3 shows a circuit diagram of a PLL system added as the W-CDMA system of the UMTS system, in the case where the multi-band radio signal transmitter/receiver is considered.
This PLL system circuit includes a quadrature modulation unit 240, a channel PLL circuit unit 241 that is a PLL synthesizer for generating an RF signal of a transmission frequency for this quadrature modulation unit 240 and a fixed PLL circuit unit 242, in a PLL configuration for a typical direct modulation.
Also, this PLL system circuit has: a mixer 243 for mixing a signal of a transmission frequency of a channel to be used from the channel PLL circuit unit 241 and an output signal from the fixed PLL circuit unit 242, and for generating a signal for a receiving local oscillation frequency; and a band pass filter 244 for limiting a band of its mixed output and extracting and outputting the signal for the receiving local oscillation frequency.
The channel PLL circuit unit 241 includes a VCO 251, a channel PLL controlling unit 252 and a low pass filter 253, and generates an RF signal of a transmission signal frequency fTX that is sent to the quadrature modulation unit 240.
The quadrature modulation unit 240 includes a mixer 254 and a mixer 255, an adder 256 and a π/2 phase shift circuit 257. The RF signal from the channel PLL circuit unit 241 is phase-shifted by the π/2 phase shift circuit 257 and sent to the mixer 254, and the RF signal whose phase is not shifted is sent to the mixer 255. Also, an I signal and a Q signal from a baseband processing unit 203 are inputted to the mixer 254 and the mixer 255, and the above-mentioned RF signals are orthogonally modulated. Respective outputs of the mixer 254 and the mixer 255 are synthesized by the adder 256 and outputted as a transmission signal from an output terminal 258.
The fixed PLL circuit unit 242 includes a VCO 261, a fixed PLL controlling unit 262 and a low pass filter 263, generates a fixed frequency signal fFIX, and sends to the mixer 243.
The mixer 243 mixes the above-mentioned fixed frequency signal fFIX with the signal frequency fTX from the above-mentioned channel PLL circuit unit 241. Then, the band pass filter 244 extracts a frequency fL0 (=fTX+fFIX) of a sum of an oscillation frequency of the VCO 251 and an oscillation frequency of the VCO 261. This is outputted as the receiving local oscillation frequency fL0 from the output terminal 245.
In a small portable wireless terminal, in order to miniaturize a circuit scale of a wireless unit, the employment of the above-mentioned direct conversion (DCR) method contributes to the miniaturization and the lighter weight. Thus, if the DCR method is used in the portable terminal of the multi-band communication system that can correspond to different two communication methods selected from systems such as GSM/DCS/UMTS and the like and the different frequency bands, it can be expected to largely contribute to the miniaturization and the lighter weight.
However, as mentioned above, in the multi-band radio signal transmitter/receiver that corresponds to the W-CDMA system and the GSM/DCS system, namely, in the circuit in which the PLL system circuit in FIG. 2 and the PLL system circuit in FIG. 3 are combined, the PLL circuit containing the VCO is doubled. Thus, its scale becomes enormous in designing the circuit and making into an IC.
The purpose of the present invention is to provide a multi-band radio signal transmitter/receiver that can achieve a miniaturization of a hardware circuit and a saving of an electric power, in view of the above-mentioned problems.